Indirect blood pressure recorder



June 20, 1961 G. D. zuxDEMA ET AL 2,989,051

INDIRECT BLooD PRESSURE RECORDER 3 Sheets-Sheet 1 Filed May 29, 1956-Nlml IN V EN TORJ.

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June 20, 1961 G. D. zulDEMA ETAL 2,989,051

INDIRECT BLOOD PRESSURE RECORDER 5 Sheets-Sheet 3 Filed May 29, 1956limite Ohio Filed May 29, 1956, Ser. No. 588,195

1 Claim. (Cl. 12S-2.05) (Granted under Title 35, U.S. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the United States Government for governmental purposes withoutpayment to us of any royalty thereon.

This invention relates to an indirect blood pressure recorder and moreparticularly to an improved means and method for taking and recordingblood pressure, as Well as pulse rate changes and the like.

The indirect taking and the recording of blood pressure readings by theinated cuff method is Well estabh lished. In a usual procedure aninflatable cult is applied over an artery in a mans arm, the cuff isinflated to a pressure in excess of the mans systolic blood pressure andgradually deflated over a period of about seconds, during which time theblood llow approaches normal for that individual. Sounds made by theblood in the artery during the described procedure are commonly detected'by the use of a stethoscope. Of particular interest are the sounds atthe systolic or peak blood pressure and at the diastolic or minimalblood pressure during the described procedures.

In practicing the above described method the cuff may be made of fabric,rubber, a flexible plastic or the like and may belinated with air, Wateror other desired fluid to a predetermined measured and controlledpressure. 'The pressure within the cut is commonly measured with amercury or an aneroid manometer. The deation of the cul'Ir is commonlyaccomplished by the manual control of the escape valve during which thesound from the stethoscope is commonly depended upon for indicating theblood pressure at the systolic and at the diastolic pressure extremes.The manual control of the escape valve is characterized by thelimitation of a nonuniform linear cui deation, which is desirable.

During the cardiac cycle it lis of particular importance to detect or toidentify that instant at which the artery obstruction which isintroduced by the inflated cuff just opens at the systolic pressure andthe instant at which the dropping arterial pressure just reaches thediastolic pressure. The sounds of blood ow through the artery during thecardiac cycle as the artery undergoes compression yand decompression bythe operation of the inflated cuff, both when detected by thestethoscope or recorded, are important sources of information to theexperimenter.

The nature of the present invention is the supplying of records of bloodpressure which are usable as a basis for the study of cardiovascularresponses from circulatory functions, inclusive of heart action. Thesubstance of the present invention is an adaptation of an inated cuiftechnique by means of a pump or a bulb for iniiating the cuif with amercury manometer indicating controlled pressure and inclusive of afirst pressure transducer connected with a recording oscillograph forrecording the pressure within the inatable cui. A pressure sensitivedevice is positioned between the inatable cuff and a skin surfaceoverlying an artery from which mechanical data is to be derived and asecond pressure transducer picks up and converts the arterial pulse intoan electrical signal which is applied preferably through a capacitor tothe same recording oscillograph where a tape is printed. The tapeproduced by the recording oscillo States Patent graph shows on a timebasis, both the cuff pressure and the arterial pressure rise and fallaccurately and perma nently recorded.

As the terms are used herein systolic pressure is dened as the point atwhich systemic arterial pressure is just suliicient to overcome thepressure within the inflated cui. In analyzing the recorded pulse waveswhich are produced by the apparatus contemplated hereby, the firstabrupt increase of the amplitude of the pulse wave, together with itschange in shape, is taken as the point of systolic pressure and thepoint of diastolic pressure is recognized by its form change and by itsdecrease in amplitude. At the systolic pressure point the pulse also ischaracterized by a Wider separation of the ascending and the descendingstrokes of the curve. A pressure sensitive device overlying the brachialartery in the arm and beneath the inflatable culi permits the detectionof pulses as they appear and disappear with pressure alterations withinthe cuff.

The blood pressure recorded which is contemplated hereby is used onhuman subjects in studies of the heart and the circulation. It has beenused successfully by the Armed Forces in supplying recordings taken fromsubjects on the human centrifuge, in high altitude pressure chambers andthe like.

An object of the present invention is the collection andk thepreservation of records indicating the cardiovascular status of asubject, particularly during the changes of acceleration and during highaltitude tlight Where cardiovascular responses are all important. Therecords so pro vided are a graphic presentation of arterial bloodpressure and pulse rate for purposes of study, comparison, andillustration.

This device provides for the automatic recording of blood pressure, andpulse rate changes using the generally accepted, recognized and wellestablished inflated arm cuff method.

In practicing the present invention preferably an electric motoroperated pump is used to inflate the cuff sufciently to occlude thebrachial artery in the human arm. The motor may be replaced by a rubberbulb if desired. The cuff is then allowed to deflate slowly preferablyat a substantially linear, uniform rate during which the pressurechanges with time are made a permanent record in a recordingoscillograph.

An illustrative embodiment of the present invention is shown in theaccompanying drawings wherein:

FIG. 1 is a diagram of an apparatus contemplated hereby as installed ona human arm;

FIG. 2 is a reproduction of an oscillograph recording of an actual pulsewave above a cuff pressure curve on time-pressure coordinates using theequipment shown in FIG. 1;

FIG. 3 is a reproduction of another oscillograph recording Where anactual pulse Wave above a cuff pressure curve is presented oncoordinates of time in seconds along the abscissa and of pressure inmillimeters of mercury along the ordinate; and

FIG. 4 is a modil'ication of the invention substituting a strain gagefor an inatable balloon shown in FIG. l of the drawings.

The equipment embodying the present invention and represented in FIG. lof the present drawings comprises a preferably automatic pump 1 whichsupplies under pressure a fluid such as air, Water or the like through ahollow tube 2 to an inilatablecuif 3. The cuif 3 is shown encircling amember or an extremity such as a human arm 4 to which blood pressurepulses are conducted through a brachial artery 5. Magnitudes of pressurewithin the cuff 3 and within the hollow tube 2 preferably are madedirectly visually observable by means of a glass walled merculymanometer 6. The manometer 6 has one leg 7 opening directly into thepressure tube 2 and has a second leg 8 which is sealed at its end remotefrom the tube 2. The mercury meniscus of the manometer is read directlyprojected against a scale 9, in indicating the magnitude of pressurewithin the cuff 3. The manometer 6 is used both in calibrating thesystem and in providing direct readings during experimentation upon asubject. A first pressure transducer 10 has a blood pressure receivingend which opens directly into the pressure tube 2 and an output end fromwhich an electrical lead 11 extends. The lirst pressure transduceroutput electrical lead 11 is connected to a recording oscillograph 12.The first pressure transducer output signals cuff pressure curves 13 and13 which are reproduced in FIGS. 2 and 3, respectively, of theaccompanying drawings.

The pressure system of the pump 1, the pressure tube 2, the cuff 3, themanometer 6 and the pressure end of the transducer 10, preferably has asafe pressure range up to at least 250 mms. of mercury. The pump 1 whichis contemplated hereby is the subject matter of a patent application nowbeing prosecuted in the interest of the H. L. Klein ManufacturingCompany of 481 East 11th Avenue, Columbus, Ohio. The pump 1 control, notshown, is adjusted to perform automatically within l or 2 seconds theinflation of the cuff 3 and then to shut off automatically upon reachinga desired pressure of illustratively 240 mms. of mercury, as indicatedby the manometer 6. Pump control then automatically allows theY fluidpressure within the system to subside along the curves 13 and 13 toambient over the next 22 to 24 seconds of a full time cycle, whichillustratively is 25 seconds long. The entire cycle of 25 secondsduration in time is repeated continuously until the procedure iSterminated by the operator.

The lirst pressure transducer 10 illustratively may be a Gauer-Wettererminiature manometer, which is described in the publications: the journalScience, for October 6, 1950, page 404, and in the journal Circulation,volume 3, page 390; a pressure transducer manufactured by andcommercially available from Statham Laboratories, Inc., Los Angeles,California under Patent Nos. 2,036,458 and 2,059,549; or the like. TheGauer- Wetterer pressure transducer described herein has a rubberdiaphragm over a piston head at the fluid pressure end of the transducerfor the purpose of confining fluid at the input end of the transducer.

The pressure values picked up by the rst transducer 10 are conducted bythe transducer electrical output lead 11 to the recording oscillograph12, where they are recorded on a tape produced by the oscillograph asthe cuff pressure curves 13 and 13', along with the pulse wave curves 14and 14', respectively, in FIGS. 2 and 3 of the drawings. The recordingoscillograph 12 illustratively may contain a 7-215 galvanometer 15,which has a sensitivity of 13 microamperes for each inch of the tape, ora galvanometer of similar sensitivity, The recording oscillograph 12illustratively may be made by the Consolidated Engineering Corporation,or by Wm. Miller Instruments, Inc., both of Pasadena, California.

Interposed between the cuff 3 and skin overlying the brachial artery 5of the arm 4, is an inflatable iiuid filled balloon or bladder 16.Preferably a thin rigid plate 16 is interposed between the bladder 16and the cuff 3. The plate 16 reduces the elasticity of the system andprovides a more accurate response on the tape produced by theoscillograph 12. The balloon or bladder 16 is shown as connected by ahollow tube 17 with a second pressure transducer 18. The second pressuretransducer 18 has an electrical output signal lead 19 preferablycapacitively coupled through a series connected condenser 21, with therecording oscillograph 12. The oscillograph 12 also contains a 7-239galvanometer 20 with the sensitivity of 4 microamps `per inch of tape.

The bladder 16 and the hollow tube 17 preferably may be made of apolyethylene plastic, rubber or the like, and preferably contain anincompressible uid, of which boiled water is a satisfactory example andwhich uid provides a direct hydraulic ram between the skin overlying thebrachial artery 5 and the thin sheet rubber diaphragm which covers thepiston head within the transducer 18. The direct current component ofthe electrical signal output from the transducer 18 preferably isblocked by the condenser 21, which may have an illustrative capacitanceof 200 microfarads. The use of a condenser of a range of from 200 to1,000 microfarads, connected in series between the transducer 18 and theoscillograph 12, is preferred. In the event a miniature manometer isused, a preferred type is backA loaded through a constriction so thatonly the alternating current component of theV blood pressure signal istransformed into movements of the diaphragm, since a carrier wave is notblocked by a condenser.

Pulse waves of arterial blood surging in the brachial artery 5 a-retransmitted by direct mechanical conduction to the hydraulic fluid whichis confined within the balloon 16 and within the tube 17. The pulsewaves in turn are applied to the pressure transducer 18 and producedisplacements of the transducer diaphragm. Displacements of thetransducer diaphragm initiate electrical signals which are conductedbetween the electrical conductor 19 and into the oscillograph 12, forpresentation upon the tape produced by the oscillograph. The pulse wavesappear on the oscillograph tape as shown in the curves 14 and 14 ofFIGS. 2 and 3 of the accompanying drawings.

The tube 17 may be omitted, if preferred, from be tween the balloon 16and the fluid pressure end of the transducer 18 for short coupling andfor simplifying this arrangement, with the rubber diaphragm closed inputtube end of the transducer 18 inserted directly through the Wall of theballoon 16. The resultant structure combines directly the balloon 16 andthe transducer 18 in a single unit which is easily and convenientlyattached to individual subjects. The short-coupled form of the inventionis immediately and accurately responsive in sense and in magnitude tominute pressure changes which are passed from the brachial 4artery totheHuid within the balloon y16.

Further simplication of the assembly results in building the balloon 16into the wall of the inflatable culf 3, or attaching the balloon 16directly to the Wall of the inflatable cuff against the skin overlyingthe brachial artery S. The resultant structure provides a singleassembly whether the transducer 18 is directly attached to the bladderor is attached to the bladder through a tube 17, as preferred.

In many of the above arrangements, pressure within the cuff 3 islapplied directly to the thin diaphragm of the transducer 10, anddisplaces it. The resulting electrical output signal is conducted by theelectrical conductor 11 to the oscillograph 12, where the cuff pressurerecordings are applied to -the oscillograph tape simultaneously with therecording of balloon or bladder pressure pulse wave recordings.

The use of the condenser 21, of from 200 to 1,000 microfarads capacity,connected in series in the pulse Wave recording output from thetransducer 18, serves to pass alternating current and to block thepassage of direct current and thereby to atten out fluctuations in thebase lines 14 and 14 of the graphs shown in FIGS. 2 and 3 of thedrawings. The presence in circuit of the condenser 21 eliminates thelarge relatively slow drop in pressure within the cuif 3, whilepreserving the smaller pulse wave displacements from within the balloon16, as indicated in the upper curves 14 and l14 of FIGS. 2 and 3,respectively, of the accompanying drawings.

The arrows 25 and 26 appearing in FIG. 3 of the drawings indicaterespectively the systolic and the diastolic configurations of thearterial blood pulse force patterns of the brachial artery 5, as theyappear on the tape of the oscillograph 12 from which readings inpressure in millimeters of mercury may be taken from the ordinate andtime in seconds may be taken from the abscissa.

Modifications of the above described means for taking and for recordingarterial blood pressures which are contemplated herein, and some ofwhich have been used lsuccessfully experimentally in the laboratory,include a metal strain gage 30. The strain gage 30 is enclosed in asubstantially fla-t envelope 31 of rubber, plastic or metal. The straingage device provides a substantially flat unit for replacing the`balloon 16 between the brachial artery 5 and the inatable cuffv 3, bothwhen the balloon 16 is separate from t-he cui and when it is madeintegral therewith. Output leads 32 from the strain gage 30 conducttheir electrical output to an amplier 33, from which leads 19 conductsignal through the capacitor |21 to the oscillograph 12, as in theearlier disclosed embodiments of the present invention.

A modiication of the strain gage concept, where the strain gage ismounted directly into and to be integral with the cu 3 toi overlie thebrachial artery 5, has the advantage of providing a single assembled cuiunit with a built-in indicator which provides simplified handling,uniformity of arm mountings, a minimizing of connections and -a minimumof error arising from manipulations and connections.

The oscillograph numbers 7-215 and 7-239 `are Consolidated EngineeringCorporation part numbers.

A preferred form of the invention which is disclosed herein and whichhas been used experimentally as an automatic recording device, has beencompared with auscultatory measurements made by trained and experiencedphysicians with favorable results. In both methods at least 20 secondswere allowed for enough pulse beats to come through for clear detectionfor both systolic and for diastolic pressures. In making theauscultatory measurements the diastolic pressure was noted in the mulingof sounds `and at the disappearance of sounds. Systolic pressure wastaken as the point at which the pulse sound was irst heard.

It is to be understood that the cuff and bladder arrangement shown inFIG. l of the accompanying drawings is an experimentally successfulmethod of operation of the present invention and that changes andmodifications described and explained herein may be made withoutdeparting from the scope of the present invention.

What we claim is:

An indirect blood pressure recorder for recording blood pressure andpulse rate changes of blood circulating in an artery of an appendagecomprising an inflatable cuff positioned around a `source of pressurechange, cui inflation means for controlling the extent of cuffinflation, means indicating the extent of cuff inflation, anincompressible Huid-filled hydraulic pressure sensitive ram deviceoverlying the source of pressure change and beneath the inatable cuif,pressure transducer means receiving its input from the pressuresensitive ram device as changes in hydraulic prsure and converting itsreceived input into electrical signal output sensitive in time and inmagnitude, an electrical signal recording means receiving the electricalsignal output Vfrom the pressure transducer means and recording in timeand in amplitude the lpressure changes to which the hydraulic pressuresensitive device is subjected, and a single piece thin rigid pressuredistributing plate interposed between the pressure sensitive ram deviceand the cuff for uniformly sustaining pressure throughout its area andthereby modifying the elasticity of the system.

References Cited in the tile of this patent UNITED STATES PATENTS1,043,521 Hoob'ler Nov. 5, 1912 2,076,642 Hubbard et al Apr. 13, 19372,272,836 Gerdien Feb. 10, 1942 2,354,818 Lippitt Aug. 1, 1944 2,447,018Keinath Aug. 17, 1948 2,536,527 Appel Ian. 2, 1951 2,555,422 Scott etal. June 5, 1951 2,615,940 Williams Oct. 28, 1952 2,634,721 GreenwoodApr. 14, 1953 2,648,328 Hathaway et -al Aug. 11, 1953 2,755,796 BouckeJuly 24, 1956 2,826,191 Burns Mar. 1l, 1958 2,837,082 Elliott et al.June 3, 1958 FOREIGN PATENTS 723,402 Germany Aug. 4, 1942

